cardboard flute - cardboard thickness
Single face displacement will only get you so far.
Just to illustrate.

Single face displacement

The image texture is used to "extrude" the original face.
Notice the incomplete rims, rough appearance, and high required geometry.
Faces: 1 000 000



Multiple Faces

Three faces on top of each other.
Displacement is used on the middle face only, to creating the wavy pattern.
Top and bottom faces have solidify modifier to add thickness.
Faces: 1000